How to set scale across all blender objects and keyframes?
Set the scale to the value you need and all the scale keyframes will be updated accordingly :

import bpy

scale = 2     #change this value  'scaling factor'

for action in  bpy.data.actions :
    for fcurve in action.fcurves :
        if fcurve.data_path == 'scale':
            for p in fcurve.keyframe_points :
                p.co[1] *= scale